Tuesday 5 June 2012

Sooty but no Sweep

Carbon Transfer Print of Dad's Shed.  Nikon D7000
5th June 2012

I have made the most of the extra days holiday today by having a printing session.

The masochistic streak in me appears to be made of soot; it is soot that I am using to do the printing and oh, how fickle it is.

The carbon transfer printing process stems back to Poitevin in 1855, and later a practical form patented by Joseph Swan (of lightbulb fame) in 1863.   Carbon transfers are still about the most archival printing method known to this day.

The process starts by mixing soot and gelatin and pouring out into a black sheet called 'tissue'.  This tissue is poured onto a carrier paper so that it is easy to handle.   Once dry, the gelatine tissue is made light sensitive by applying potassium dichromate and then squashed together with the image  negative and exposed to ultraviolet light.

The now 'cooked' tissue is soaked in water and then squeegeed onto a piece of water colour paper (which has been previously coated with a mix of gelatine and formaldehyde) and left to rest for a while.  As the sandwich rests, the water moves between the wet paper and carbon tissue and (hopefully) sticks the two together.

The fun bit comes next.  The sandwich of papers is then placed in a bath of hot water, whereupon the soot-laden gelatine starts to melt; it is interesting watching the gelatine ooze out of the sandwich as in the picture below.
Soot laden gelatine starting to melt.  Nikon D7000

After a few minutes, whilst holding ones breath, the carrier paper is stripped from the sandwich, hopefully leaving the now dissolving carbon tissue stuck firmly to the watercolour paper; this is often where the first volley of expletives get propelled across the kitchen as chunks of the image stick to the carrier sheet and not the other paper.

The image is currently a black mass of dissolving goo.

Black mass of dissolving gelatine.  Nikon D7000

The paper is then floated face down in the hot water for about 15 minutes and hopefully all the gelatine that was under the dense parts of the negative and did not harden with the UV light detach and sink to the bottom of the tray.  The next round of expletives is if the image also detaches and sinks!

A dark version of the final image should now be visible.  With longer soaking, more and more of the gelatine falls away until the final image is left, ready for drying.

Partially developed image.  Nikon D7000
The wet carbon print has a very interesting characteristic; the more UV light hit the gelatine when being exposed, the thicker the layer (and so the more soot) that is left.   The result is that a strong relief image is visible in the wet print (as in the image below).   Some carbon printers strive to get as thick a relief as possible so that even when the image is dry, there is still some textured relief visible.

With the watercolour paper I use, there is little or no relief left when it is dry; apart from the odd lump of course ground soot that is.

The process makes nice pictures, but is not an ideal printing approach if you are vegetarian (them bones them bones, boil them bones .....)

EDIT: 8/7/12, I have added a page describing the process in much more detail here.

Gelatine relief in wet print.  Nikon D7000

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